The concept is to use modules similar to shipping container modules on earth.
The elements of the system and different uses of modules are
* Depots – fuel and other supplies
* Propulsion Unit
* Crew Module
* Cargo modules
* Service Modules
Any given orbit planes needs its own systems. It can be as difficult to make major orbit and plane changes as re-launching from earth.
Increased low-cost access to space will increase the demand for more infrastructure in space. The more people in space means more needs for lifeboats and places to evacuate.
Modularity and standardized connections and docking will provide flexibility and enalbe redundancy.
The modules need to live and stay in orbit. The only resource being used up is the fuel.
The designs require modules that are only launched once with low delta vee.